Some conventional motor drive apparatuses have a plurality of motor drive parts. According to an electric motor drive apparatus disclosed in the following patent document 1, for example, a motor driver and a motor winding form a motor drive part and two motor drive parts are provided. Thus, the motor is operated to generate drive force, whichever winding of the motor drive part is energized.
According an electric power steering apparatus disclosed in the following patent document 2, when failure occurs in one of three-phase windings of a three-phase brushless motor, the motor is operated by energizing the remaining two of the three-phase windings, which are normal.
Patent document 1: JP H7-33033
Patent document 2: JP 2009-6963 (US 2010/0017063A)
In case of generating large rotational torque by arranging a plurality of motor drive parts in the motor drive apparatus of patent document 1, a large current need be supplied to the motor. The motor drive parts therefore are required to control large currents. If certain failure occurs in the motor drive apparatus for some reasons, a large current will unexpectedly flow. It is therefore general practice to start driving the motor after checking for any failure in each of the motor drive parts.
In case of generating rotary force from the motor by using only two phases in the motor drive apparatus of patent document 2, a failure portion in the motor drive parts need be specified before driving the motor. It is also required to check whether any other failure is present after specifying the failure portion. Thus, the failure detection processing, which is performed before starting to drive the motor, is complicated. If such complicated failure detection processing is used in a motor drive apparatus having a plurality of motor drive parts, a large and expensive microcomputer will be required to perform the complicated failure detection method a number of times.